Study On Efficient Extraction Method Of Relieving Pressure Gas In Directional Long Borehole Of Floor

China’s Energy Development Report 2022 shows that coal consumption accounts for56.2%of total energy consumption,and the safe development of the coal industry is related to the sustainable development of China’s energy.Gas disaster is a serious threat to the safety of coal mine production,and the relief mining effect of protective layer is better in gas control measures.After the mining of overlying coal seam,the depressurized gas gushed out from the underlying coal rock mass,which is usually extracted by drilling through the stratum in the bottom pumping roadway,requires the construction of one more floor roadway and the drilling workload is large.At present,the new technology of directional long drilling is widely used,with high construction flexibility.It can be used to extract pressure relief gas from the underlying coal rock mass and save the construction roadway quantity.However,there are few researches on pressure relief gas extraction from directional long boreholes of floor.Therefore,it is of great theoretical and practical significance to carry out research on efficient extraction method of pressure relief gas from directional long boreholes of floor.In this paper,8₂37 working face of Qidong Coal Mine is taken as the research object,and the depressurization area of coal rock mass under the change of mining stress is analyzed theoretically,and the permeability equation is combined to determine the permeability change in mining.Combined with the migration equation of gas in coal seam and rock layer,a depressurization gas migration model is established.COMSOL software was used to simulate the pressure relief process of 8₂ coal mining on the underlying coal rock mass,and the variation rule of gas pressure under different distance of single borehole into the goaf,as well as the influence of different extraction aperture and negative pressure on the gas pressure in floor crack was analyzed.It is found that with the change of distance between borehole and goaf,gas extraction effect presents a downward trend,and the extraction radius decreases from 2.7m to 2.2m when borehole enters goaf from-50m to 0m.The extraction radius increases sharply from 2.2m to 10m during the period from 0m to 100m,reaching the highest point at 100m.The pumping radius decreased from 10m to 3.5m between 100m and300m.With the increase of extraction aperture,gas pressure decreases.Increasing the borehole has marginal effect.Increasing the borehole at equal distance slows down the reduction of gas pressure.In practical engineering application,0.09m borehole can meet the needs of extraction.The negative pressure of extraction increases and the gas pressure decreases,but the effect is not obvious.In practical engineering application,10～20k Pa can meet the needs of extraction.It is found that the linkage between boreholes is weaker when the spacing of boreholes is too large,and the utilization rate of single borehole is lower when the spacing of boreholes is too small.The spacing of 5-7m is appropriate.The simulation results are applied to the field practice,and the extraction effect of pressure relief gas in the directional long borehole of bottom plate of 8₂37 working face is investigated.It is found that the closer to the middle of the goaf,the better the drilling and extraction effect,and the pressure relief time in the middle area is earlier than that in the edge position.The variation trend of extraction effect of each borehole is consistent with the simulation law with the increase of the distance into the goaf.After the initial pressure,floor pressure relief produces a large number of cracks,and gas is enriched in the cracks with high concentration,so the extraction effect of borehole here increases significantly.After entering the goaf,it is delayed with the evolution of cracks.Practice has proved that 8₂37 working face adopts floor oriented long borehole to intercept 9 coal pressure relief gas effect is good.In the process of working face mining,the gas extraction rate reaches 86.5%,the maximum concentration of return air gas is 0.64%,and the maximum concentration of upper corner gas is 0.76%,which ensures the safe and efficient mining of coal seam.Figure[71]table[4]reference[52]...